Antibody Formats

Antibody Formats

Trends in clinical development of monoclonal antibodies indicates that there is a nascent shift toward the study of antibody fragments and it is likely that antibody fragments are going to be the next important class of protein-based therapeutics after monoclonal antibodies. Antibody fragments [fragments], in particular the scFvs, Fabs and VHH/VH retain full antigen-binding capacity and superior properties for research, diagnostic and therapeutic applications. Fragments are particularly useful in applications where epitope binding is sufficient for the desired effect including therapeutic applications such as virus neutralization or receptor blocking.

The smallest antigen binding fragment that retains its complete antigen binding site is the Fv fragment, which consists entirely of variable (V) regions. A soluble and flexible amino acid peptide linker is used to connect the V regions to a scFv (single chain fragment variable) fragment for stabilization of the molecule, or the constant (C) domains are added to the V regions to generate a Fab fragment [fragment, antigen-binding]. scFv and Fab are widely used fragments that can be easily produced in prokaryotic hosts. Other Ab formats include disulfide-bond stabilized scFv (ds-scFv), single chain Fab (scFab), as well as di- and multimeric antibody formats like dia-, tria- and tetra-bodies, or minibodies (miniAbs) that comprise different formats consisting of scFvs linked to oligomerization domains. The smallest fragments are VHH/VH of camelid heavy chain Abs and single domain Abs (sdAb). For most therapeutic applications, however, the Fc portion of an Ig is essential as it is instrumental in mediating cytotoxic effector functions such as ADCC and CDC.

Antibody Formats

Figure 1: The modular domain architecture of Igs has been exploited to create a growing range of alternative antibody formats that spans a molecular-weight range of at least 12–150 kDa and a valency (n) range from monomeric (n = 1), dimeric (n = 2) and trimeric (n = 3) to tetrameric (n = 4) and potentially higher1. The building block that is most frequently used to create novel antibody formats is the single-chain variable (V)-domain antibody fragment (scFv), which comprises V domains from the heavy and light chain (VH and VL domain) joined by a peptide linker of ~15 amino acid residues.

Fab Antibody, scFv, VHH/VH Advantages

The previous section in this series is “Antibody Basics”. To review, click here.

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